Microorganisms belonging to the genera Alcaligenes, Pseudomonas, Achromobacter, Aerobacter, Bacillus and Brevibacterium are known as microorganisms producing L-aspartic acid from maleic acid and ammonia, and some of them have already been applied for patents (Japanese Patent Publication Nos. 2793/1963, 11993/1967, 11994/1967, and 8710/1968).
Two kinds of enzyme, that is, maleate isomerase and aspartase, are involved in conversion of ammonium maleate into L-aspartic acid, where aspartase is relatively stable, while maleate isomerase is unstable and its activity is inherently liable to reduction in particular by oxygen.
Further, the stability of this maleate isomerase varies depending on the strain, and if the microorganism is immobilized for use, the half-life of the activity is short and satisfactory production is not attained under the present circumstances.